1) Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a substrate polishing apparatus for polishing a wafer or substrate in the process of fabricating a semiconductor integrated circuit.
2) Description of the Prior Art
In conventional chemical-mechanical polish (CMP) tools, the wafer is secured and spins on a horizontal orientation while pressing against a CMP polish pad to achieve a global planarization. Due to the total thickness variation (TTV) of the wafer, the contour of the incoming wafer can be concave, convex, taper or of any other irregular pattern. As a result of this wafer the total thickness variation (TTV), subsequent film deposition will follow this contour, hence resulting in non-uniform film thickness after chemical-mechanical polish (CMP). This problem can arise due to the conventional top ring design, whereby a constant down force is applied to the entire wafer causing localized wafer warpage. Hence, this results in very poor material removal uniformity.
Equipment manufactures are trying to solve this non-uniformity problem by introducing more advanced and complex top rings with variable backside pressure on different zones of the wafer. All these measures add cost and have limited effectiveness. Conventional polishers also suffer from non-uniform slurry distribution where less slurry is delivered the wafer center as compared to the wafer edges. This results in higher polish rates on the edges.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering: U.S. Pat. No. 5,542,874(Chikaki), U.S. Pat. No. 5,928,062(Miller et al.), U.S. Pat. No. 6,183,345B1(Kamomo et al.), U.S. Pat. No. 6,203,408B1(Quek), U.S. Pat. No. 6,234,868B1(Easter et al.), U.S. Pat. No. 6,159,083(Appel et al.), U.S. Pat. No. 6,273,796B1(Moore), and U.S. Pat. No. 6,241,585B1(White) that show CMP polisher designs.
However, these polisher designs can be further improved.